Reinforcement ribs for wound articles are often important as a means of preventing inward or outward collapse of the side walls of the articles due to mechanical pressure thereon and in our GB2256420 we disclosed a method of forming the reinforcement ribs integrally with the remainder of the structure by sequentially interposing between the helical windings straight windings along the length of the intended rib with the object being to form a rib of substantially triangular shape, ideally having a height about two or three times the intended base of the triangle so as to produce the required stiffness. However, in practice it has been found that winding individual straight fibres in this way within the helically wound fibres makes them tend to spread out to form a flattish band rather than a required rib of height sufficient to provide the required stiffness.